Mazda Forum - Mazda Enthusiast Forums - NGK Spark ruthenium hx

NGK did not state NOT to use anti seize but to use their exact wording

NGK does not recommend using thread anti-seize on their spark plugs

The reason most spark plug manufactures now state "recommend" and not require this is because to many people (including mechanics) were not using anti seize correctly on spark plug threads. This led to in some cases spark plug misfiring and or broken spark plugs. Which can happen with or without anti seize but mostly from DIY not paying attention to the socket angle and spark plug position when installing it. The number one damage often not quickly detected is cracking the spark plug insulator. Also, some breaking them from over tightening them. When anti seize used correctly it can save damage to the spark plug threads in the head, make removing and installing spark plugs easier and create a better protection against spark plug cross threading. Common sense when installing the spark plugs pertaining to tightening. Recommending not using anti seize on spark plug threads was another big reason spark plug companies did not want to have to answer to broken spark plug and claims of engine damage from the end users. Most spark plugs are in 2 categories of installing with and without a torque value. Many newer engines and spark plugs have the snug down and turn 1/4 to 1/2 more or as indicated on the spark plug box. Many just refer you to the owners or vehcle service manual.
Do what you feel the most comfortable with when choosing to use or not use anti sieve on the threads. And use common sense when torquing them down.

Never take recommendations of the spark plug number from any source except directly from the spark plug manufactures application guide or the service information of your vehcle under spark plug information or to contact your dealership parts department.
Aways be aware that even with spark plugs there can be updates to the part numbers so look for the parts cataloging last update information to be absolutely sure you are getting the latest part numbers.
Doing any other method of confirming the exact and proper spark plug number could cause expensive damage to your engine.

I always use anti seize on my own spark plugs and every customer vehcle I have worked on in over 40+ decades without any issues whatsoever.